1. Field of the Invention
This invention generally relates to a motor. More specifically, the present invention relates to a motor such as a spindle motor having hydrodynamic beatings, the spindle motor adapted to be provided in a disk-driving device for rotationally driving a data storage media such as a hard disk. The present invention also relates to a method for manufacturing the motor.
2. Background Information
FIG. 1 is a cross sectional view of a spindle motor (an electric motor), provided with hydrodynamic bearings that make use of the dynamic pressure of a lubricating fluid, for driving at least one data storage medium such as hard disk. The spindle motor depicted in FIG. 1 is described in detail in co-pending application Ser. No. 09/267,621, filed Mar. 15, 1999, now U.S. Pat. No. 6,066,903. The content of and disclosure in U.S. Pat. No. 6,066,903 is hereby incorporated by reference in its entirety.
The spindle motor depicted in FIG. 1 includes a stationary shaft 12 fixed to a base 10 and a rotor 11 rotatably supported by the stationary shaft 12 via hydrodynamic bearings. A lower end of the stationary shaft 12 is fixedly fitted in a coupling bore of a base 10 (base portion).
The stationary shaft 12 includes two main components: a stationary shaft portion 12a which extends rigidly upward from the base 10; and a stationary thrust plate 12b which is an annular plate member fixedly and coaxially fitted to an upper portion of the stationary shaft portion 12a.
The rotor 11 includes a rotary sleeve 18 that fits over the outer periphery of the stationary shaft 12 with a gap defined between opposing surfaces of the stationary shaft 12 and of the rotary sleeve 18. The rotary sleeve 18 includes a cylindrical rotor hub 18a and an annular rotary thrust plate 18b fixedly fitted into a portion of the rotary sleeve 18.
A hard disk (not shown) of a hard disk drive is carried on an outer peripheral portion of a cylindrical surface of the cylindrical rotor hub 18a.
The rotary thrust plate 18b is fixedly fitted in a large inner diameter portion 18a4 to partially define a thrust bearing gap 20 around the stationary thrust plate 12b. The thrust bearing gap 20 is defined between the opposing surfaces of the stationary and rotary thrust plates 12b and 18b and between the surfaces of the stationary thrust plate 12b and the side and bottom surfaces of a recess formed within a middle inner diameter portion 18a3 of the rotary sleeve 18. Above the rotary thrust plate 18b in the large inner diameter portion 18a4, an annular plate-shaped seal member 22 is fixedly fitted in place.
The radially inner portion of the surface which partially defines the upper portion of the thrust gap 20, specifically, the radially inner portion of the bottom or lower inclined surface 100 of the rotary thrust plate 18b, is tapered such that the lower inclined surface 100 of the rotary thrust plate 18b is inclined upward toward the center of the stationary shaft 12. As a result, an air space 29 defined between the lower inclined surface 100 of the rotary thrust plate 18b and the upper flat surface of the stationary thrust plate 12b progressively increases toward the center of the stationary shaft 12 to form a tapered seal of an upper thrust bearing 40.
A radially inner portion of the surface of the rotary sleeve 18 is formed with a tapered surface 20a that is inclined downward toward the radially inner direction thereby defining a tapered seal of a lower thrust bearing 42.
Lubricant 44 is provided as needed in the gap between the stationary shaft 12 and the rotary sleeve 18, in particular in the regions depicted in FIG. 1. The lubricant 44 is retained at each respective position by the above described tapered seals, and in particular as a result of the surface tension created on the surface of the lubricant 44.
The effects of surface tension in the lubricant 44 cause formation of a meniscus in each exposed portion of the lubricant 44, for example between the lower inclined surface 100 and the adjacent surface of the stationary thrust plate 12b. The meniscus, in effect, defines an interface between the lubricant 44 and air. There are upper and lower interfaces defined by the meniscus of the lubricant 44 in the annular gaps between the walls defining the thrust bearing gap 20 and the surfaces of the stationary thrust plate 12b. The upper and lower interfaces face radially inward at the air space 29 and first oil separating space 32. An annular oil-free space 46 is defined at an inner periphery from the lower interface (lower meniscus) of the lubricant 44 at the first oil separating space 32.
On an inner peripheral surface of the stationary thrust plate 12b, an axial groove is formed. When the stationary thrust plate 12b is fixedly fitted on the stationary shaft portion 12a, the axial groove defines a breathing bore 48 between the outer peripheral surface of the stationary shaft portion 12a and the inner peripheral surface of the stationary thrust plate 12b. The breathing bore 48 connects the annular oil free space 46 to the air outside of the spindle motor via the annular space 31, a gap between the outer peripheral surface of the stationary shaft portion 12a and the inner peripheral surfaces of the rotary thrust plate 18b, the lubricant catching groove 30, and a gap between the outer peripheral surface of the stationary shaft portion 12a and the seal member 22. The breathing bore 48 has a cross sectional size that is large enough so as not to be closed by the lubricant 44 due to surface tension. The breathing bore 48 can be formed at a plurality of positions of the stationary thrust plate 12b.
An upper radial bearing 56 and a lower radial bearing 58 are formed by herringbone groove portions 54 and 55, respectively, of the inner peripheral surface of the journal portion 18a1 and the portions of the outer peripheral surface of the stationary shaft member 12a that face the herringbone grooves 54 and 55. The upper radial bearing 56 is located immediately beneath the first oil separating space 32. The lower radial bearing 58 is located between the air space 28 and a second oil separating space 62.
An air communication or conduit bore 64 is formed inside the stationary shaft portion 12a. The bore 64 includes a lower opening 64a which is open to the lubricant 44 in the lower radial bearing 58, and the bore 64 includes an upper opening 64b which is open to the second oil separating space 62. The lower opening 64a is disposed in the proximity of a boundary between the lower radial bearing 58 and the air space 28. The upper opening 64b is disposed in the proximity of a boundary between the upper portion and the lower portion of the second oil separating space 62.
The spindle motor described above is typically assembled by first inserting a lower portion of the stationary shaft portion 12a into the rotary sleeve 18 such that, for instance, only the portion of the shaft portion 12a below the upper opening 64b is inserted into the rotary sleeve 18. Lubricant, such as the lubricant 44, is applied to the portion of the shaft portion 12a proximate the upper opening 64b. Thereafter, the shaft portion 12a is lowered into the rotary sleeve 18 thereby drawing and spreading the lubricant down into the portions of the rotary sleeve 18 which subsequently form the radial hydrodynamic bearings 56 and 58 and the lower thrust bearing 42. Lubricant 44 is also applied to the upper surface of the thrust plate 12b after completely inserting the thrust plate 12b and shaft 12 into the rotary sleeve 18. Next, the rotary thrust plate 18b is fitted to the opening of the rotary sleeve 18 above the thrust plate 12b. The rotary thrust plate 18b and the rotary sleeve 18 are adhered to one another by, for instance, adhesive or glue.
However, in the above described spindle motor, the contacting surfaces 18s1 and 18s2 of the rotary sleeve 18 and the rotary thrust plate 18b are adhered to one another with adhesive after the lubricant has been applied to surfaces of the shaft 12 and thrust plate 12b. The lubricant, which is a lubricating oil, sometimes tends to migrate between the contacting surfaces 18s1 and 18s2 due to a capillary action. As a result, the adjacent surfaces 18s1 and 18s2 can become contaminated with the lubricant resulting in the lack of adhesion of the adhesive between the surfaces 18s1 and 18s2. In such circumstances,.the rotary sleeve 18 and the rotary thrust plate 18b may not be satisfactorily adhered to one another leading to leakage of lubricant.
In view of the above, there exists a need for a motor and a method of manufacturing a motor which overcome the above mentioned problems in the prior art. Especially, the present invention provides a motor in which the rotary thrust plate and the rotary sleeve are more reliably adhered to one another easily and tightly, thereby preventing reduction in productivity. The present invention also provides a method of manufacturing such motor. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from the following disclosure.